Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

Originator's data acquisition and analysis

Discrete samples were taken either using a CTD water bottle rosette. Discrete samples were subsampled and passed through a mixed ester membrane (Whatman WME, pore size 0.45 µm; pre-soaked in dilute HCl and rinsed with water). All analyses were conducted using a nutrient autoanalyser made up of Technicon MK II single channel colorimeters and Ismatec pumps and custom built reaction manifolds.

Nitrate Determination of nitrate was conducted following the method described by Stainton (1974). Nitrate is reduced to nitrite by passing the sample stream through a transmission tube containing a copper-coated cadmium wire. Nitrite ions diazotise sulphanilamide then couple with N-1-naphthylethylenediamine dihydrochloride to form an azo-dye, the concentration of which is measured by absorbance at 550 nm.

Phosphate Phosphate concentration was determined following a method similar to that described by Tréguer and Le Corre (1975). Orthophosphate ions react with acidified ammonium molybdate in the presence of antimony to form phosphomolbdic acid. This is reduced by ascorbic acid to a 'molydenum blue' complex (Riley and Skirrow, 1975) the concentration of which is measured by absorbance at 630nm.

Silicate The concentration of silicate in seawater was determined using a method based on an industrial method by Technicon (1976). Silicate ions react with ammonium molybdate in acidic conditions producing silicomolybdic acid. This is reduced to a 'molybdenum blue' complex by ascorbic acid (Riley and Skirrow, 1975) and its concentration is measured by absorbance at 660 nm.

Ammonium Ammonia is determined using a variant of the Berthelot reaction. Sodium dichloroisocyanurate is used as a hypochlorite donor (Krom, 1984) and catalysis is performed by potassium ferrocyanide. After reagent additions, the reaction stream is heated to 40°C and formation of 'indophenol blue' is promoted under longwave UV radiation (365 nm). Concentration is measured by absorbance at 630 nm.

See Whitehouse, 1997 for full details of all instrumentation and analysis involved.

BODC Data Processing Procedures

Data were received by BODC in spreadsheet format with the nutrient data from various BAS cruises in labeled worksheets (BAS_nutrient_data_1981-2009.xls). The following metadata fields were also included with the data: cruise ID, date, latitude, longitude, event number and pressure.

Parameter codes defined in the BODC parameter dictionary were mapped to the variables as follows:

Nutrient data were received with no associated time for the sampling event. It was therefore deemed necessary to acquire times from the cruise event log, using the event numbers to map the correct times to the nutrient sampling events.

The depth of the water column at each sampling event has been assigned using GMT and GEBCO data .

The data were banked according to BODC standard procedures for sample data. Data were banked as received, with no averaging or other modifications applied.

Data Quality Report

Dynamics of Ocean Management- DYNAMOE

Introduction

DYNAMOE was created in order to provide data for the global management of finfish communities, squid and krill and avoid future long-term damage from over-fishing. The understanding of how the ocean ecosystem works provides scientists with the tools to predict how human activity and climate changes will affect the Southern Ocean environment and how biological communities will respond. This programme will cover a period from March 2000 to April 2005 and is part of the British Antarctic Survey research programme Antarctic Science in the Global Context.

The research will be concentrated on the Scotia Sea, particularly the food-web and fishery dynamics around South Georgia using the sampling facilities on the RRS James Clark Ross, including vertical profiling for temperature and salinity measurements, sensory and acoustic systems for ocean currents measurements and plankton, fish and squid mapping and nets for biological specimens.

The land-based studies will take place at Bird Island, South Georgia following a year-round study of seabirds and marine mammals which will provide an assessment of breeding performance, growth, diet and foraging.

The programme will integrate interdisciplinary studies in population and food webs modelling, as well as develop satellite-tracking capabilities to link the land-based predator studies to the ship-based ocean analyses.

This programme encompasses two projects:

Dynamics of pelagic organisms in Southern Ocean ecosystems

Dynamics of predators and fisheries in Southern Ocean ecosystems

Scientific Objectives

The main objectives are:

Develop a spatial analysis of how the Southern Ocean ecosystems work

Quantify the importance of ocean currents in the transport of biological material in the Southern Ocean food-webs

Examine how Southern Ocean ecosystems respond to variability and change, focusing on links between krill and predators

Develop an ecosystem approach to the management of Southern ocean fisheries

Data Availability

Data sets collected during this project are available to the academic community.

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.